Spectral analysis of hearing protector impulsive insertion loss.
Cameron J Fackler, Elliott H Berger, William J Murphy and 1 others
PMID 27885881WHAT IT FOUND
For hearing protectors tested, peak reduction varied with the impulse source, but frequency-based attenuation agreed across methods.
Frequency-based attenuation described protector performance more completely than peak reduction.
Key findings
01The level-dependent earplug showed greater peak reduction as impulse level increased.
02Frequency-based attenuation agreed between the two impulse sources for the foam earplug and the level-dependent earplug.
03Real-ear attenuation at threshold tended to give a conservative estimate of frequency-based attenuation.
STILL TO COME
How it was doneWhat they found
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What it does not show
The AR-15 impulses rose and returned in about 0.3 to 0.5 ms, below the 0.5 to 2.0 ms range required by the standard. Shock-tube testing at the lowest level used 140 dB, not the 132 dB called for by the standard. The artificial ear can measure attenuation above what human ears can achieve, and the paper states there is no correction for this in peak reduction measurements. The outdoor 132 dB AR-15 measurement for the electronic earmuff may have been affected by reflections because trees were nearby. Only three hearing protectors were tested, so the results do not describe all devices used in practice.
Declared interests
Cameron Fackler, Elliott Berger, and Michael Stergar are employed by 3M, the manufacturer of the hearing protectors studied in this work.
The easy way to misread this
Do not assume the measured peak reduction equals the protection a person will receive. The artificial ear can produce attenuation values above what human ears can achieve, and the paper gives no method to adjust peak reduction for bone conduction.